I like clean desktops without icons dumped on it by software without asking me first (Adobe! HP printers! too many others!).
I love it when I don’t get useless messages about updates (Microsoft! Adobe! Java! manufactors!).
I love it when I don’t get bothered by anything popping up in front as I’m working (messengers! so called “support assistants”!).
I like to customize the desktop, simple colours of my own choosing, no icon cluttering.
I love it when the OS or programs don’t patronise me (wanted a real professional administrator’s version of Windows for years).

That’s why I ended up with fluxbox as my desktop after some time using Gnome 2, KDE 3.x and the later 4.x series.

Over the years I’ve used Linux (Debian), Free- and OpenBSD professionally because they were the right tool for the job. I’m using open source professionally to support customers whenever it does the job.
Nowadays having to use a Windows (or even a Mac) machine annoys me because it just gets in the way of doing my job.
There are some good reasons to use these, but generally I prefer no-nonsense open source software.

Some of the reasons behind my choices;

-simplicity
I prefer to use the old-fashioned XMMS as music player because it does the job in a clean interface without taking up a lot of screen real estate. No successor comes close, not even Audacious which is my only alternative. Same with MPV for playing video, Links 2 for browsing, XFE for file management and nano for writing.

-customizing
I want to be able to change more than five or six colours in the interface. I want to exclude items I don’t need or think are distracting me from what I want to do.
I use fluxbox with several virtual desktops each dedicated to a certain function. Administration (root terminal), internet things (browsers), remote connections for work (FreeRDP, X2go, SSH), media (audio, video), projects I’m working on, etc.. Which is why I disabled the taskbar because I know where I have to be and I don’t waste space with it.
I use Links whenever I can (it’s so relaxing to browse the internet without flash ads or animations and other distractions and just get to the content that matters), Firefox for sites that can’t provide a clean interface. Firefox is still the best choice because it can be customized with necessary addons like oldbar and status-4-evar to prevent the annoying default behavior pretending it’s Chrome (as one person once said; “If I wanted to use Chrome, I would have installed Chrome.”). I do wish they made a current Firefox version that looked like the clean and simple 3.6.

-update when I want to
Don’t bother me with messages about updates constantly! Either provide the option to do it automatically or shut your gob and let me do it when I want to. And no, I don’t want to be informed updates have been installed if it’s done automatically by my choice. I only want to know when the update procedure has failed after some time and it has become more urgent. Not right away. Not after a few days. When it’s *really* urgent.

-troubleshooting
So many times I wished the OS (yes you, Windows) or program would output plaintext logs whenever something goes wrong. It would make it so much easier to find out what’s wrong. Telling me it’s an unknow error doesn’t help *cough*Windows update*cough*. As long as some error message is blurted out into text I, and I’d say we, system administrators, can get our jobs done much easier.
I won’t get into the systemd debate on the Linux side of things but I do think they’ve made some proprietary choices which makes me look at the Debian fork in the future.

I love the UNIX philosophy of tools having one function only and doing it well instead of one tool doing everything mediocre. Anything complex that needs to be done can be better done by a chain of tools which are easier to debug than one tool that just blurts out the wrong output. (I used to build Doom and Quake levels by scripting the different tools and compensating for bugs in the output)